I have a chance to pick this up for cheap, needs tires and the gear on the cranks that drives the cam is worn and it keeps slipping out of time (so I'm told)
I kinda know the guy and he is no mechanic, had local yami mech do it on the side, told him it needs a $650 crank.
I can get a new crank for @175 and I see used for $40 and up.
Suposed to have run fine for a few mins the died.
I see all the engine parts still listed and it appears yamaha used this engine for many years after 1987. So parts should be available????

How about the rest of the bike, any known problems. I don't see the shaft drive parts still anymore going back that far, so that is concern perhaps. Brakes brearing starter etc (common stuff) seem readily available.

How big a job is the crank swap? Just crank, rings, gasket kit needed or ???

I see manuals available online for $5 so that would be the first purchase, but just wondering if its worth fixing or if i should forget it.
The back tires are down to about 1/4 of tread so it was at least used that much. Plastic, seat and overall is real nice, apears the head light is missing thou. Kinda a hole in the front there.
Thoughts?

Thanks
Ken

 

Well drug this home to look it over. Told guy I'd let him know in a day or two.
Not sure where the yami mech was coming from with the bad crank causeing the timing to slip. After looking at the manual the only gear related to timing is the sprocket the chain runs on and as near as I can see the cam is in time. Chain is tight and looks good.
Mech told seller he had it running, after re timing it, but it slipped after a few starts...

I found water in the carb, a intake valve that hissing back into the air cleaner. Only 90 psi compression, book say 142lb min and 171lb standard. Squirting oil into the cylinder brought it up to 125.
So now I'm not sure if it needs a valve job and bored/oversized piston or just the valve.
I checked the valve lash and the rockers are not tight.
The engine won't even cough or fart so far. Do motorcycle engine need more compression then a car engine. I though maybe I could make it run a bit with the oil in the cylinder but nothing.

Anyone with experience on these, can one get away with lapping the valves, or do they usually need guides, valve and machining. A new complete (i think, likely less cam) head can be bought for $247, cylinder is $105, Piston and rings $55, Gaskets $30 from Yamaha.

This bike needs rear tires, key switch, and the shifter was welded to the shift rod. Shifter is stripped, and the shift rod is stripted on the outside.

Plastic is nice, original seat cover is perfect, not banged or bent up anywhere. It was the air filter cover that was off, but seller gave it to me.
Where is the best place to look for parts?
Should a machine shop be able to do a valve job for less then a new head?
Whats the odds on the bottom end needing work?
The shaft drive seems fine, this is the ones they packed with grease, not oil filled where they pretty reliable? As so far I don't see new parts available for these.
Ken

 

actuly the slipping can be the gear on the crank...like the mech said. It also sounds like you need rings. ill help you out with this i had mine sinse 86 there great. Take it one question at a time though.

 

Sorry to over do it, lots to learn. Manual is the best $ I spent.

How would I test to see if the cam sprocket is slipping??

I still can't believe the mech ever had it running with the compression that low.

Well I pulled the head, inverted it and filled the chamber with gas, exhaust holds but intake leaks.
So I'm calling my machinist in the morning to enquire about $$ and parts needed for valve job.
Hopefully grind and good to go.

Bore looks good, no ring ridge, some staining 1/2 way down, but looks very good overall. Exhaust pipe was not full of burnt oil, pretty clean.

I see new jug with piston, rings, circlip and gaskets for $140. But i think given the the minimal time to pull the top end, that I'll just do the valves and see where compression comes to and if and how it runs. I can always do the piston & jug later if need be.

The next bigest concern at this point appears to be a stripped shifter that was un welded from shift rod.
Thanks
Ken

 

You can test it by holding cam chain TIGHT and crank it if its working it will rip it outta ur hand.
U should probly do the valves. If you can get a leakdown done that would be great.

 

Sorry i forgot about shift rod but you shuld just buy one off ebay.

 

Well then I did it right I think, I will try one more time.
Before pulling it down, I had the side cover off the head and I could definitely hear more air escaping past the intake valve then the rings as I turned it over by hand.

 

Sounds like a money pit. A machine like that running has low resale value. Could be a good learning experience for you.

 

You definitly need to do the valves than any yama tech shuld know it off the top his head.

 

Don
You might have a point, would not even think about it if I did not like to tinker. Likely only worth 800 to 1k running (I see your in Canada to, so you know things cost more here)
If the bore was wore bad I'd be thinking about parting it, but it really has no ring ridge so I think hours are low. If I can keep it running without to much grief it will be good enough for my boys to tool around here on. Better then the 2 china quads I have now for them. (figure if I can keep those running I can fix this)
Ken